They are generally much more power hungry than the equivalent ASIC, built using the same process. However if your aim is to emulate a sufficiently old ASIC then

They are generally much more power hungry than the equivalent ASIC, built using the same process. However if your aim is to emulate a sufficiently old ASIC then you can probably beat it with a modern FPGA. And there are FPGAs aimed at low power consumption: they are just also slower.